Use your muscles or you’ll lose them

The past two weeks, I discussed sarcopenia, the degenerative loss of muscle mass. It’s not a disease, and it can occur in healthy people, and the primary cause is sedentary living.

The axiom “use it or lose it” is perfectly applicable to sarcopenia. The key is making your muscles do things they don’t want to do, pushing them out of their comfort zone. In turn, this sends a message that your muscles are important and you want to keep them around. In contrast, when you don’t use your muscles, you send a message that they are not important. In response, your body quits supporting your muscles with energy, which causes them to atrophy (shrink). So the harder you work your muscles, the more your body appreciates them.

But how hard is hard? This is the essence of many of the questions I receive. There is not an easy answer to this, and you must decide how much you are ready and willing to do. With that in mind, it may be helpful to take a peek under the skin and see how muscles operate.

Fast-twitch and slow-twitch fibers

There are three types of muscle in the body. Our concern is skeletal muscle, the kind that moves the joints, like the biceps muscle in your arm. Skeletal muscle makes up about 42 percent of the total body mass in males, and 36 percent in females.

A skeletal muscle is made up of a variety of different muscle cells (also called fibers) that exist side by side in a mosaic pattern, like different colored tiles in a floor. To simplify, the two main categories are fast-twitch and slow-twitch fibers. Slow-twitch fibers react more slowly when stimulated by a nerve, and they are less powerful. They are used for everyday activities that are not too demanding, like walking. In contrast, fast-twitch fibers are the powerful fibers used for lifting, jumping and other power movements.

Recruiting muscle fibers

Slow-twitch fibers are always recruited first, and the body hopes to use as few as possible to get the job done. So when you lift your arm, or open a door, or pick up a book, you are using a small number of slow-twitch fibers contained within the muscle. If the task is more demanding, the number of slow-twitch fibers recruited will increase to meet the demand. And if the task is very demanding, the body will be forced to bring the fast-twitch fibers into play.

With this in mind, you can see that on an everyday basis, most muscular activity is restricted to a small number of slow-twitch fibers. This means the rest of the slow-twitch fibers and the fast-twitch fibers are rarely called upon to perform. They are neglected, in other words, and when muscle cells are not used, they first atrophy (shrink), and eventually they fade away.

The challenge, then, is to regularly involve as many slow-twitch and fast-twitch fibers as you can to let them know you care about them and want to keep them around. This, in turn, begs the question, how can you engage all of these muscle fibers? The answer is through resistance training (lifting weights). And the best way to know if you are doing enough is to push the muscles to mild exhaustion. You can do this with lighter weights (more repetitions) or heavier weights (fewer repetitions). Regardless, just keep going until the muscle tells you it can’t do any more.

You have to do more than just go through the motions, in other words. (Note: Before going down this road, be sure to get the OK from your doctor.)

The bottom line is, your muscles are your friends. Keep them around by making them uncomfortable two or three days a week.

Next week, I’ll discuss the distinction between building muscle versus maintaining it.

Bryant Stamford is professor and chairman of the department of kinesiology and integrative physiology at Hanover College. To contact him, email stamford@hanover.edu.